A display device using a light-emitting element (organic EL element) in which an organic compound is used as a light-emitting substance has been developed rapidly as a next generation lighting device or display device because it has advantages that such a light-emitting element can be formed to be thin and lightweight, has very high response speed for input signals, and has low power consumption.
In an organic EL element, when a voltage is applied between electrodes with a light-emitting layer interposed therebetween, electrons and holes injected from the electrodes recombine to form an excited state, and when the excited state returns to a ground state, light emission is obtained. Since the wavelength of light emitted from a light-emitting substance is peculiar to the light-emitting substance, use of different types of organic compounds for light-emitting substances makes it possible to provide light-emitting elements which exhibit various wavelengths, i.e., various colors.
Light emitted from a light-emitting substance is peculiar to the substance, as described above. However, important performances as a light-emitting element, such as lifetime and power consumption, are not only dependent on the light-emitting substance but also greatly dependent on layers other than the light-emitting layer, an element structure, properties of a light-emitting substance and a host, compatibility between them, and the like. Thus, it is true that many kinds of light-emitting element materials are necessary for a growth in this field. For the above-described reasons, light-emitting element materials with a variety of molecular structures have been proposed (e.g., Patent Documents 1 to 3).
The substance named 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA) is one of materials which can be used as a transport material or a host material of a light-emitting layer in a light-emitting element. By using CzPA as a host material or an electron-transport material, a light-emitting element which provides blue fluorescence and has very excellent characteristics in terms of emission efficiency, driving voltage, and lifetime can be manufactured.